The president's claim stems from Amazon's practice of not collecting sales tax from its third-party platform sales outside a select few states. The practice, Trump alleges, puts "many thousands of retailers" out of business, unable to survive against Jeff Bezos' ever-growing consumer titan.

"It's unfair relative to the [other] retailers," Mnuchin argued. "That's money — by the way — that states need for infrastructure and very, very important for the states' economies."

The third-party business represents roughly half of Amazon's unit sales, according to Stifel.

"They've absolutely dominated the retail business, they've put tons of retailers out of business," Mnuchin said. "The president is focused on Amazon and the economic issues that are impacting retailers all around the country."